The invention concerns a closure clip and a process for the production of closure clips of strip-form or wire-form material for closing tubular or bag-like packagings, wherein a substantially wave-form profile with successive first and second apex points is stamped along the strip-form or wire-form material. The first apex point forms a clip bottom, flanks respectively adjoining the first apex point on each side thereof form clip limbs which are bent over in a U-shape and the second apex point, with respect to the U-shape, forms outwardly bent-over limb ends at which two adjacent closure clips are separably connected. The invention further concerns a stamping tool for the production of closure clips in accordance with such a process.
Closure clips of that kind are known for example from DE 3 148 757 A1, EP 0 337 301 A1 or EP 0 738 662 A1. Those closure clips (also referred to as clips) are used to close tubular or bag-shaped packagings filled with liquid to viscous-pasty or (in part) granular content, sausage cases or artificial cases, at one or both ends thereof. For that purpose, the clips, typically made from an aluminum wire extrusion, are pre-bent in a U-shape in a clip machine, as described above, and are fed to a first closure tool of the clip machine, the female die, in a condition of being joined together by means of connecting legs formed in the form of the bent limb ends. After the filled packaging has been constricted in portion-wise manner to form a plaited portion, for example, by means of a displacement member or by being twisted off and thus a portion (sausage) has been divided off, the foremost clip of the above-described line of clips is pressed against the plaited portion and clamped between that and the female die. Thereupon, by means of a second closure tool that moves towards the female die, the punch, the foremost clip is severed from the following line of clips in the region of the connecting leg and then closed around the plaited portion of the packaging material. In that situation, the bent limb ends are pressed against the outside of the clip limbs and bent around the plaited portion of the packaging material, the limb ends and leg portions being pressed in butting relationship against each other and are upset so that the result is a ring that compresses the plaited portion of the packaging material as closely as possible.
The endeavor was and is to develop such closure clips in such a fashion that either with the material thickness remaining the same, an always greater retaining force and resistance to slipping is achieved in order to ensure that the closure effect is as firm and tight as possible or conversely, with the same quality of closure, it is possible to make a saving in terms of material. Particularly when using plastic skins, for example of PVC, polyamide, polyester or plastic-coated fiber skins that have a relatively smooth surface, the resistance to slipping is a major requirement.
For that purpose DE 3 148 757 A1 proposes, for example, arranging a reinforcing bead that is disposed centrally with respect to the width of the strip of material, in the region of the clip bottom and the arcuate connecting portions provided at the transition to the clip limbs. The reinforcing bead increases in particular the resistance of the closure clip to its being bent open.
EP 0 738 622 A1 proposes a different route, whereby the closure clips, on the inside, have one or more grooves in the longitudinal direction of the strip of material in order to reduce the risk of the clips slipping off. EP 0 337 301 A1, along the same line, further discloses closure clips that on the inside of the clip limbs and also on the clip bottom have a plurality of grooves that substantially provide surface coverage and are arranged in mutually crossing relationship. The knurled patterns produced in that way have a higher level of surface roughness in relation to the longitudinal grooves and further reduce the risk of slipping off.